International Telecommunications Union (ITU) G.711 Appendix I is an algorithm for packet loss concealment (PLC). An objective of PLC is to generate a synthetic speech signal to cover missing data (i.e., erasures) in a received bit stream. Ideally, the synthesized signal can have the same timbre and spectral characteristics as the missing signal, and may not create unnatural artifacts. In the ITU G.711 PLC algorithm, when erasures last longer than 10 ms, more than one pitch segment is introduced to generate the synthetic signal, and an extra overlay-add (OLA) is included just after the 10 ms boundary. This extra OLA may not be necessary, and can require more CPU activity, with a possible degradation in voice quality.
In ITU G.711 PLC implementation, a 3.75 ms buffer delay may be required to generate a pitch OLA segment before the erasures for a smooth transition. The pitch can range from 5 ms to 15 ms, which may be suitable for relatively low density digital signal processor (DSP)-based applications. However, as more voice applications are developed on general-purpose X86-based appliances, this algorithm can introduce higher CPU requirements. Accordingly, products such as Meeting Place Express, Lucas, Manchester, or other voice servers or similar products, may benefit from improvements to the G.711 algorithm.